1. Field of the Invention
This invention generally relates to handling natural gas at a natural gas facility. More specifically, the present invention relates to a natural gas handling system that stores liquefied natural gas (LNG) and converts liquefied natural gas (LNG) to warm high pressure and medium pressure compressed natural gas (CNG) without the use of pumps or compressors. In addition, the present invention can provide a source of cold in that the heat of vaporization of LNG represents 220 Btu""s/pound of energy and the sensible heat of the vapor represents approximately 0.5 Btu""s/pound degrees Fahrenheit.
2. Background Information
Deregulation of the natural gas industry has created the need for complete system solutions relating to the handling of natural gas, especially the handling of liquefied natural gas (LNG) and compressed natural gas (CNG). One of the least-polluting fuels is natural gas. Moreover, the cost of natural gas is very competitive when compared to other fuels, which are currently available on-the market. Thus, natural gas is an environmentally friendly and cost effective alternative to other fuels which is being given a high priority by government and industry due to it""s easy access and long term availability. Natural gas is commonly used in two different forms, i.e., compressed natural gas (CNG) and liquefied natural gas (LNG).
The use of compressed natural gas (CNG) as a fuel for motor vehicles has been known for many years, and is in use in many areas of the world. One obstacle to the use of compressed natural gas vehicles is the cost to process clean CNG to a re-fueling station from the nearest natural gas pipeline. In the past, the conventional manner for handling the natural gas is to filter and compress natural gas from the pipeline and then transport the natural gas to the re-fueling stations. However, transportation of the natural gas can be expensive, since natural gas often contains impurities or stations need to be located in areas with no pipelines.
It has also been demonstrated that natural gas can be liquefied and stored in refrigerated vessels for transportation, as described in U.S. Pat. No. 3,232,725. The method requires refrigeration equipment and insulation to hold the gas in a sub-freezing temperature during transportation.
The use of LNG has become very common in the Northeast area of the United States. In fact, the process is not new. The liquefaction of natural gas dates back to the early 1900""s. LNG has been used as a vehicle fuel since the mid 1960 s. LNG is produced in a liquefaction plant where natural gas is liquefied, stored in an insulated storage tank, and, when needed, is pumped out of the tank as a liquid, heated in a vaporizer or re-gasifier and delivered to the pipeline or distribution system at a compatible temperature and pressure. The technology came out of NASA""s space program. There are approximately 100 LNG facilities in the United States that can serve as hubs for many satellite facilities such as the present invention.
When natural gas is cooled to a temperature of approximately xe2x88x92260xc2x0 F. at atmospheric pressure, it condenses to a liquid (LNG). One cubic foot of liquid is equal to 618 cubic feet of natural gas found at a stove-top burner. Application of heat to the liquid natural gas at its latent heat of 220 BTU""s per pound causes vaporization and expansion to occur. If the liquid natural gas is confined during the application of heat to the liquid natural gas, then this reaction will provide the requisite 5000 psig for CNG storage. LNG weighs about 55 percent less than water. LNG is odorless, colorless, non-corrosive, and non-toxic. When vaporized, it burns only in concentrations of 5 percent to 15 percent when mixed with air. Neither LNG, nor its vapor can explode in an unconfined environment.
In the United States, the Department of Transportation (DOT) regulates the transportation of LNG as well as the drivers of the trucks. The double-walled trucks are like xe2x80x9cthermos-bottlesxe2x80x9d on wheels. They transport LNG at minus 250 degrees F. LNG can be stored up to three days in the tanks of the trucks without losing any LNG through the boil-off process. The inner tanks of the trucks are made of thick aluminum designed to withstand up to 100 pounds of pressure. There is a steel outer shell around the outside of the inner tank. The tanks are designed to withstand most accidents that may occur during the transportation of LNG.
During the years of controlled testing by independent laboratories and hundreds of thousands of gallons (intentional) spilled LNG, ignition of a vapor cloud has yet to cause an explosion. In fact, some testing involved initiating the combustion of the gas cloud with high explosives. The strength of the detonation was no stronger than that delivered by the explosives. Thus, the ignition of LNG or LNG vapor will not cause an explosion in an unconfined environment. Natural gas is only combustible at a concentration of 5 to 15 percent when mixed with air. And, its flame speed is very slow.
Currently, there are approximately 39 satellite and approximately 55 liquefaction facilities in the United States. In other countries, there are approximately 81 satellite and approximately 14 liquefaction facilities. Since deregulation of the natural gas industry, the construction of LNG facilities in the United States has increased.
There exists a need for new modular technology to provide clean and accessible fuel for remote compressed natural gas supply by liquefied natural gas trucking that does not rely upon complicated and maintenance intensive systems. Most conventional natural gas handling systems today rely upon compressors and pumps to move and/or convert the liquefied natural gas to compressed natural gas.
In view of the above, there exists a need for a natural gas handling system which overcomes the above mentioned problems in the prior art. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
An object of the present invention is to provide a new modular natural gas handling system to provide clean and accessible fuel for remote compressed natural gas supplied by liquefied natural gas trucking.
Another object of the present invention is to provide a natural gas handling system that does not rely on complicated systems.
Another object of the present invention is to provide a natural gas handling system for converting liquid natural gas to compressed natural gas that does not require maintenance intensive systems.
Another object of the present invention is to provide a natural gas handling system that provides cooling source using the latent heat and sensible heat as a source for refrigeration.
The foregoing objects can basically be attained by a method of handling natural gas comprising the steps of cooling a storage unit by supplying liquefied natural gas thereto; removing low pressure natural gas vapor from the storage unit; supplying liquefied natural gas to the storage unit to a predetermined level within the storage unit; and heating the storage unit to convert the liquefied natural gas within the storage unit to compressed natural gas of a predetermined pressure; and supplying the compressed natural gas at the predetermined pressure to a compressed natural gas unit.
The foregoing objects can also be attained by providing a natural gas handling system comprising a LNG/CNG storage unit having a predetermined capacity and a predetermined pressure rating, the LNG/CNG storage unit having an inlet line with a first on/off valve to selectively receive liquefied natural gas, a first outlet line with a second on/off valve to selectively deliver low pressure natural gas, and a second outlet line with a third valve to selectively deliver compressed natural gas; a first heat exchanger operatively coupled to the storage unit to heat liquefied natural gas contained within the storage unit; a level detection indicator operatively coupled to the storage unit to indicate a predetermined level of liquefied natural gas contained within the storage unit; a first pressure regulator coupled to the first outlet to allow natural gas vapor to be removed from the storage unit upon reaching a first predetermined pressure; and controls operatively coupled to the first and second on/off valves to selectively open the first and second on/off valves during filling of the storage unit, and to selectively close the first and second on/off valve when the liquefied natural gas in the storage unit reaches the predetermined level as indicated by the level detection indicator.
These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention.